1. Field of the Invention
This invention relates generally to the demonstration of photoactive properties, such as hydrophilicity, on a surface and, more particularly, to a method and kit to demonstrate and/or simulate one or more photoactive properties of a surface in the absence of or at low levels of activating radiation.
2. Technical Considerations
Photoactive substrates have found widespread acceptance in many fields. These photoactive substrates can be photocatalytic and/or hydrophilic (such as photohydrophilic). By “photoactive” or “photoactively” is meant the capability to generate one or more physical or chemical effects upon exposure to certain wavelengths of electromagnetic energy. These effects can be caused, for example, by the photogeneration of an electron-hole pair when illuminated by activating radiation of a particular frequency. The activating radiation is typically in the ultraviolet (UV) or visible ranges of the electromagnetic spectrum. By “UV range” is meant electromagnetic radiation in the range of 280 nanometers (nm) up to 395 nm. By “visible range” is meant electromagnetic radiation in the range of 395 nm to 800 nm. By “photocatalytic” is meant a surface, such as a coating, having self-cleaning properties. By “self-cleaning” is meant a surface which upon exposure to electromagnetic radiation in the photoabsorption band of the surface material (i.e., activating radiation) interacts with organic contaminants on the surface to degrade or decompose at least some of the organic contaminants. By “hydrophilic” or “hydrophilicity” is meant water wetting. By “photohydrophilic” or “photohydrophilicity” is meant a surface upon which the contact angle of a water droplet decreases with time as a result of exposure of the surface to electromagnetic radiation within the photoabsorption band of the surface (e.g., coating). By “photoabsorption band” is meant the range of electromagnetic radiation absorbed by a material to render the material photoactive. For photohydrophilicity for example, the contact angle of a water droplet on the surface can decrease to a value less than 15°, such as less than 10°, and can become superhydrophilic, e.g., decrease to less than 5°, after exposure to activating radiation in the photoabsorption band of the material for a time period and at an intensity sufficient to activate the material.
While photoactive articles, such as architectural windows having a photoactive surface or coating, provide advantages over non-photoactive articles, problems can arise in demonstrating such photoactive properties and/or articles to a potential customer. For example, many of the commercially available photoactive windows are “UV photoactive”, meaning that the windows exhibit photoactivity only upon exposure to electromagnetic radiation in the UV range. Since only about 3% to 5% of the solar energy that reaches the earth's surface is in this wavelength range, the photoactive window to be demonstrated may have to be exposed to solar energy for a sufficient period of time to activate the window before the photoactive properties of the window can be demonstrated to a customer. Other windows are “visibly photoactive”, meaning that their photoabsorption band is at least partly in the visible range. By “activate” is meant to expose the photoactive surface to electromagnetic radiation within the photoabsorption band of the photoactive material for a period of time sufficient for the photoactive material to begin to display photoactive properties, such as but not limited to photohydrophilicity and/or photocatalytic activity. This can mean having to maintain a demonstration window outdoors at a particular location and require potential customers to come to that location during daylight hours (when the window is active due to the presence of solar radiation) to demonstrate the benefits of the photoactive surface to the customer. Should it be desired to demonstrate the photoactive window to a customer during the nighttime or indoors, a light source, such as a conventional mercury or black lamp, may be required to provide sufficient energy to render the window photoactive. Such problems are compounded if it is desired to have a salesman visit various customers' locations with a demonstration substrate (such as a sample of a photoactive window or a photoactive substrate) to demonstrate the photoactive properties of the substrate to customers. The salesman may keep the demonstration substrate in his car (such as in the trunk or other areas where the substrate is not accessible to solar energy) and, hence, degrade the photoactivity level of the substrate surface to the point where the photoactive material no longer displays one or more photoactive properties, such as hydrophilicity and/or photocatalysis. This degradation can be caused, for example, by a build-up of contaminants on the surface. Moreover, it would be difficult to demonstrate the photoactive window at night or indoors without requiring the salesman to carry a portable light source to activate the substrate to photocatalytically degrade contaminants on the surface.
Therefore, it would be advantageous to provide a method of demonstrating or simulating at least some of the photoactive properties of a photoactive surface in the absence of or at low levels of activating radiation. It would also be advantageous to simulate at least some photoactive properties, such as hydrophilicity, on a non-photoactive surface.